Art of cracking hydrocarbons



Jul 26, 1932. E. c HERTHEL ART OF CRACKING HYDROCARBONS Filed April 4, 1930 Patented July 26, 1932 UNITED STATES PATENT OFFICE EUGENE C. HERTHEL, OF FLOSSMOOR, ILLINOIS, ASSIGNOR '10 SINCLAIR REFINING COM- PANY, OF NEW YORK, N. Y., A CORPORATION OF MAINE ART OF CRACKING HYDROCARBONS Application filed April 4,

This invention relates to improvements in the method of producing lower boiling hydrocarbon oils, such as gasoline, from higher boiling hydrocarbon oils, such as gas oil and 5 reduced crude oil, by cracking operations,

The present invention provides an 1mproved method and apparatus of special value and application for heating hydrocarbon oils to cracking temperatures in carrying out operations in which high boiling oil is heated to a cracking temperature under high pressure and in which the hot oil products of this heating operation are separated into a vaporized fraction and an unvaporized fraction under lower pressure, or so-called pressure coil cracking operations. The

improved method and apparatus of the invention, however, are of general application for heating hydrocarbon oils to cracking temperatures.

In one aspect, this invention comprlsesa modification of the invention described in my application filed April 4, 1930, Serial No. 441,553.

According to this invention, the oil is heated to the cracking temperature by circulation thru a plurality of heating tubes in a heating chamber arranged with respect to the combustion chamber in which fuel is burned 30 for supplying heat to the operation, so that the heating tubes in the heating chamber are heated both by sensible heat absorbed from the heating gases from the combustion chamber, the hot gaseous products of combustion, and by radiant heat transmitted directly from the combustion chamber to the heating chamber, a stream of recirculated heating gases being utilized as a battle to prevent flame impingement on the heating tubes in 0 the heating chamber by compelling the heating gases from the combustion chamber to pass to the heating chamber along a path substantially longer than, that along which radiant heat is transferred from the combus tion chamber to the heating chamber.

1930. Serial No. 441,554.

The invention will be further described in connection with the accompanying drawing which illustrates, diagrammatically and conventionally, in elevation and partly in section and with parts broken away, one form of apparatus embodying the invention and adapted for carrying out the invention.

In carrying out so-called pressure coil cracking operations in the apparatus illustrated, for example, a stream of high boiling oil is forced, by means of pump 1, thru the heating tubes 2, connected to form a continuous heating conduit, arranged in the heating chamber 3, the hot oil products from the heating tubes 2 being discharged thru connection 4', including a pressure regulating and reducing valve 5, to a suitable vapor separatin receptacle, the oil being heated to a crac ing temperature during passage thru the heating tubes 2. Oil cooler than the hot oil products discharged thru the connection 4 may be introduced thru the connection 6, to arrest the cracking reaction initiated in the heating tubes 2, and supplied to the vapor separating receptacle with these hot oil products. In the heating tubes 2, the oil may be heated to a temperature approximating 87 5-97 5 F.,

under a pressure approximating 200-600 pounds per square inch, as discharged there from, for example.

The furnace of the apparatus illustrated comprises the heating chamber 8 and the combustion chamber 7, this heating chamber and this combustion chamber being partially separatedby a low bridge-wall 8. Radiant heat is transmitted directly from the combustion chamber 7 to the heating chamber 3 above the bridge-wall 8. The hot gaseous products of combustion from the combustion chamber, however, are compelled to pass upwardly for a substantial distance above the bridge-wall 8 so that they enter the heating chamber 3, generally, near its upper end by introduction of a stream of recirculated heating gases upwardly over, and outwardly from, the face of the bridge-wall 8 toward the combustion chamber 7. The heating gases so introduced into the upper end of the heating chamber 3 then pass downwardly therethru, escaping thru the duct 9. Part, usually the major part, of these gases is introduced upwardly across, and outwardly from, the face of the bridge-wall 8 toward the combustion chamber 7, as just described, thru ducts 10 and 11 by means of the fan 12, the remaining part of these heating gases being discharged thru the stack flue 13. The damper 1a is provided in the stack flue 13 for purposes of control. Fuel and air are supplied to the combustion chamber in the usual manner by means of the burner 15 in the apparatus illustrated. The air for combustion may be preheated by heat exchange, in the exchanger 16, with the heating gases escaping thru the .stack flue 13.

In the apparatus illustrated, radiant heat is transmitted along a relatively short path directly from the combustion chamber 7. The sensible heat of the hot gaseous prod cts of combustion is also transferred to the heating chamber 3 by passing these heating gases therethru, but these heating gases are passed from the combustion chamber 7 to the heating chamber 3 along the path substantially longer than that along which radiant heat is transferred from the combustion chamber 7 to the heating chamber 3, a path long enough to avoid flame impingement upon the heating tubes 2.

The recirculation of heating gases thru the heating chamber, in accordance with this invention, is further advantageous in minimizing any tendency toward local overheating within the heating chamber and in improving the rate of absorption of sensible heat therein. The use of preheated air for combustion, in conjunction with this invention, is particularly advantageous in that it improves the rate of transmission of radiant heat from the combustion chamber to the heating chamber by afifording higher combustion temperatures.

The heating chamber may be provided with a baffle 17 as described in my application filed February 8, 1930, Serial No. 426,901 now U. S. Patent 1,809,297. The baffle 17, of the refractory metal such as any of the well known heat resistant alloys for example, is arranged generally parallel to the bridgewall 8 subdividing the heating tubes 2 into two groups, the one group between the bailie l7 and the bridge-wall 8 and the other group on the other side of the baffle 17. The battle 17 extends entirely across the heating chamher but is arranged to leave passages for heating gases across the upper and lower ends of the heating chamber. By adjusting the areas of these passages and the relative areas of these passages, the ratio between the rates at which heat is-absorbed by the first group of heating tubes and by the second group of heating tubes may be increased or decreased.

The particular arrangement of apparatus illustrated is of special value and application in carrying out operations in which oil is to be brought quickly to a high cracking temperature and then maintained at that tem perature or at a temperature progressively increasing or decreasing therefrom for a fixed period of time. The oil is supplied first to the group of heating tubes absorbing heat at the highest rate, those most exposed to radiant heat, the group of heating tubes between the baii'le 1. and the bridge-wall 8, and is then passed thru the remaining heating tubes. The oil is thus brought quickly to a high cracking temperature in a region in which the heat absorption rate is high and is then circulated thru heating tubes in a region in which the heat absorption rate is lower.

The advantages of the invention include particularly improvements in both capacity and efiiciency. claim:

In heating hydrocarbon oils to crackk temperatures, the improvement which comprises burning fuel in a combustion chamber, transmitting radiant heat from said combustion chamber directly to a heating chamber, passing hot gaseous products ct combustion from said combustion chamher to said heating chamber and compelling them, in such passage, to pass along a path substantially longer than that along which radiant heat is transmitted to said heating chamber and long enough to avoid flame impingement upon heating tubes in said heating chamber by introduction between the combustion chamber and the heating chamber of a stream of recirculated heating gases withdrawn from the heating chamber, and circulating oil thru a plurality of heating tubes arranged in said heating chamber, thereby heating the oil to a cracking temperature in the heating tubes in said heating chamber both by sensible heat absorbed from the heating gases from the combustion chain er and by radiant heat transmitted directly from the combustion chamber.

2. In apparatus for heating hydrocarbon oils to cracking temperatures, a combustion chamber and a heating chamber arranged to permit direct transmission of radiant heat from the combustion chamber to the heating chamber, means for withdrawing heating gases fromtheheatingchamber,meansfor recirculating heating gases withdrawn from the heating chamber andintroducin gthem between the combustion chamber and the heating chamber to compel hot gaseous products of combustion to pass from the combustion chamber to the heating chamber along a path substantially longer than that along which radiant heat is transmitted from the com- 

